The present invention concerns compositions useful in the preparation of catalysts, the catalysts and the polymerization of olefins employing these catalysts.
Dual transition metal compounds containing both chromium and titanium have been employed in the preparation of catalysts for olefin polymerization in U.S. Pat. Nos. 3,752,795 and 3,847,957. Such dual transition metal compounds are formed by reacting a tetraorganotitanate with chromium oxide.
Typically, catalysts in which a chromium compound is employed to polymerize ethylene show a sizable response to both hydrogen and temperature. As a result, most catalyst systems containing chromium must be run at low reaction temperatures (i.e., slurry conditions) to prevent the formation of large amounts of undesirable low molecular weight waxes or high melt index polyethylene.
It has now been discovered that compounds prepared from chromium oxide and a tetravalent zirconium compound can be employed in catalysts suitable for the polymerization of olefins which show a low hydrogen response and which can produce polyethylene having a high molecular weight at high reaction temperatures (i.e., solution conditions).